The invention relates to herbicidal products based on esters of bromoxynil and/or ioxynil.
Herbicidal products of the type concerned comprise, as active substance, mixtures of bromoxynil and/or ioxynil esters and are in the form of solutions of these esters in solvents, advantageously in the presence of surface-active substances adapted to render them dispersible in water for their application by spraying.
These solutions of bromoxynil and/or ioxynil esters in solvents comprising surface-active products are denoted by the term "emulsifiable concentrates".
Herbicidal products of the type concerned are already known which are based on 3.5-dibromo-4-hydroxybenzonitrile n-octanoate (or bromoxynil n-octanoate) and/or 3.5-diiodo-4-hydroxy-benzontirile n-octanoate (or ioxynil n-octanoate); the principal use of these products resides in the destruction of dicotyledon adventitious species in the post-spearing or sprouting phase of cereal cultivation; it is recalled moreover that bromoxynil n-octanoate is a waxy, cream colored solid of melting point 45.degree.-46.degree. C. when it is pure and 36.degree.-40.degree. C. when it is of technical quality and that ioxynil n-octanoate is a waxy solid of cream to brown colour, of melting point 59.degree.-60.degree. C. when it is pure and 50.degree.-55.degree. C. when it is of technical quality.
These herbicidal products have the drawback, for reasons of behaviour at low temperature, of not permitting concentrations, for products of commercial quality, higher than 240 g of bromoxynil or ioxynil equivalent per liter since, at the latter concentration, the corresponding solutions of bromoxynil or ioxynil n-octanoate crystallize at -7.degree. C. and, for example, at 480 g/l, the crystallization starts from 20.degree. C.
Now, the crystallization temperature of solutions or of emulsifiable concentrates of bromoxynil or ioxynil esters is a limiting factor for the concentration of these products since, on the one hand, these products are often manufactured and stored in winter and, on the other hand, the crystalline product is very difficult to reliquefy and it remains in any case heterogeneous and hence unsuitable for any subsequent use.
To overcome this drawback, it has already been proposed, in the case of herbicidal substances of the type concerned which are based on bromoxynil n-octanoate (French Pat. No. 84 19489) to incorporate with said products a substantial proportion of bromoxynil heptanoate, due to which it becomes possible to provide products containing up to 500 g/l of bromoxynil equivalent without crystallizing at -7.degree. C. for herbicidal properties very similar to those of the products based on n-octanoate alone.
It has also been proposed (U.S. Pat. No. 4,332,613) to incorporate with said herbicidal products a substantial proportion of bromoxynil and/or ioxynil n-butyrate. Here again, the crystallization point is lowered to a value below -7.degree. C. for concentrations which can reach 600 g/l of bromoxynil and/or ioxynil equivalent. Concentrations ranging up to 800 g/l are provided but not preferred since they do not ensure an absence of crystallization at -7.degree. C.
Applicants have made it their particular objective, to do better and to provide herbicidal products of the type concerned which, for concentrations of a bromoxynil and/or ioxynil equivalent higher than those of the prior art, have a freezing point lower than, and at the most equal to, that of known products.
And they have found that this objective could be achieved through herbicidal substances of the type concerned comprising in solution, in solvents and preferably in the presence of surface-active products, admixtures of straight and branched acid esters of bromoxynil and/or ioxynil.
These products show, surprisingly and unexpectedly, cold behaviour characteristics improved with respect to those of products formed from bromoxynil and/or ioxynil octanoate alone or in admixture with the other linear acid esters described in the above-identified patents.
And still more surprisingly and unexpectedly, these products formed according to the invention show phytoactivities equivalent to those of the prior art products despite the well-known fact (see for example the article of B. J. Heywood which appeared under the title "Hydroxybenzonitrile Herbicides" in the issue of 19 Nov. 1966 of the review "Chemistry and Industry") that the branched acid esters of bromoxynil and ioxynil show very low phytoactivity, and even practically nil.